Generally, it is known in the art of printing presses to equip a blanket cylinder with a device for covering the gap in the cylinder. A common disadvantage of such prior art devices is that the gap cover does not give optimum protection against penetration by liquid detergents used for cleaning the cylinders, or penetration by water or ink-water emulsions. Another typical problem is that the gap-covering device disposed in the gap cannot adequately compensate the imbalance of the rotating blanket cylinder, because the mass of the gap-covering components is insufficient in size and distribution to counteract the dynamic imbalance.
In the prior art, it is admittedly known from DE-OS 3 110 982, for example, to provide filler members in the gap of a blanket cylinder. It is also known from DE-PS 3 540 581, DE-OS 3 644 501, and DE-PS 3 705 594 to dispose a rail-like supporting bar along the entire length of the gap and secure it to the base thereof. These devices, however, do not seal the gap in optimum manner against penetration of detergents or the like, because the gap cannot be reliably sealed on all sides. In addition, these filling members or supporting bars are clearly intended only for reel presses, where the blanket cylinders have a narrow gap, and are consequently unsuitable for blanket cylinders for sheet-fed rotary offset presses, which have a wide gap covering about 90.degree. of the cylinder circumference.
In DE-AS 2,707,643 a rounded cap-like member is disposed to partially cover the gap of a blanket cylinder. However, because this cap member is also disposed to engage and tilt open the clamping bars on the blanket holding spindles, substantial openings leading into the gap are left unsealed.